Metallic lithographic oven



NOV. 1, 1938. R BYRON METALLIC LITHOGRAPHIC OVEN Filed Jan. 9, 1935 3Sheets-Sheet 2 QQ Q mwg

| 1 I T I I I I IIEI N ATTORNEY NOV. 1, 1938. R BYRON 2,134,906

METALLI C LITHOGRAPHI C OVEN Filed Jan. 9, 1935 3 Sheets-Sheet 5INVENTOR ATTORNEY Patented Nov. 1, 1938 UNITED STATES METALLICLITHOGRAPHIC OVEN Ralph Byron, New York, N. Y., assignor to J. 0. RossEngineering Corporation, New York, N. Y., a corporation of New YorkApplication January 9, 1935, Serial No. 1,006

3 Claims.

This invention relates to an oven for baking or drying metallicllthographed or coated sheets.

In the making of metal lithographed sheets or in allied industries wheremetal is,coated it is necessary after coating to dry or bake the sheetsand to cool them in order to fix the coatings and to permit subsequenthandling. Many of the inks or coatings contain volatile solvents whichhave a fuel value and sometimes are of an explosive nature when insufiicient concentration. The metal sheets that are used are thin and inconsequence are not easily handled. The drying or baking must be of sucha nature that the sheets are uniformly dried and within closetemperature limits due to the natureof the inks or coating. In caseswhere the solvents give ofi volatile gases it is not desirable toexhaust them to the atmosphere and yet they are generally of such anature that a temperature of too high a 20 degree must be used to burnthem for that temperature to be utilized in the oven or dryer. Thetemperature utilized in a dryer of this type is generally below 450Fahrenheit, while the autoignition temperature of many of the vaporsgiven off in the solvents ranges from 700 to 1100 Fahrenheit. Hence, ifan attempt is made to utilize the fuel value of the solvents thetemperature of the heating medium will be too high. I propose to utilizethe heating value of the gases arising from the drying of the plateswithout using the same gases as a circulating heating medium.

In any dryer there is the necessity for the proper control of thetemperature of the circulating drying medium. Such proper control isalmost impossible where a single source is utilized with a unitary pointof distribution. In addition, in order to keep the cost of operation aslow as possible, the heater must be operated and also the fuel contentof the solvents should be recovered and used as fuel and further thewaste heat from the air and gases in the device should be utilized.

One of the objects of my invention is to pro vide a satisfactory dryeror oven for metal printed or coated sheets wherein a proper atmosphereat a proper temperature may be maintained throughout the dryer.

Another object of my invention is to utilize the fuel content of thesolvents and other volatiles given off during the drying without injuryto the materials being dried.

Still another object of the invention is to add at its greatest fuelefficiency and lowest heat loss' fresh air to the circulating heatingmedium to improve the quality of the finished product.

A still further object of this invention is to I provide a dryer formetallic coated or printed sheets and the like that will utilize theheat con- 5 tent of the fuel efficiently while at the same time usingthe fuel value of the solvents and the heat content of the waste air andvolatiles from the oven.

Other objects will appear more fully hereinafter.

In carrying out my invention, I propose to provide a dryer wherein themetallic sheets are supported by finger bars or wickets'on an endlesscarrier; the wicket or finger bars being spaced approximately an inchand a quarter apart. The closeness of the spacing is necessitated by therequirement of compactness on the part of the dryer and whichrequirement increases the difficulty of both the drying and the cooling.A single heater is utilized. This heater is what is known as theindirect type, that is, one wherein the products of combustion (heatingmedium) are not permitted to intermingle with the drying medium which isgenerally air.

With my invention, the heater is run at a higher temperature than isrequired for the drying medium to be furnished within the oven. Thismakes it possible to burn the volatiles drawn from the dryer in thecombustion chamber of the indirect heater. In addition to their fuelvalue, the temperature of the gases is in the neighborhood of 300Fahrenheit, which compared with the normal average temperature ofcombustion air operates to increase the thermal efficiency of theheater. The heating medium is led to mixing boxes'at stationsdistributed lengthwise of the dryer. At the stations are located blowersor fanshaving connection wih the mixing boxes and connections withopenings below the carrier 40 for the metallic sheets. At each stationin the top of the dryer are conduits leading to the mixing boxes. Inaddition, there are fresh air openings in the mixing boxes. Dampers areplaced in the three conduits leading to the mixing boxes whereby thetemperature within each mixing box may be controlled automatically. Forinstance, if the temperature adjacent one unit drops, the damper opensin the line of the connection to the heater permitting relatively hightemperature air to be admitted to the mixing box thereby raising thetemperature of the circulating medium at the station. The fresh airinlet to the mixing box, I have shown as manually controlled.

If desired, it may be automatically controlled to r conjointly act withthe automatic damper or valve from the heater, that is, when the heatervalve is opened the fresh air valve might be closed or vice versa. Inpractice, I have found that due to the plenum pressure of the heatingmedium and the suction pressure of the fan or blower at the station,sufficiently quick action is obtained in raising or lowering thetemperature in the mixing chamber without the necessity of the automaticcontrol -of the fresh air inlet. The admixture of fresh air at thestations is particularly desirable by reason of the fact that thecirculating medium should contain oxygen and if the gases from the ovenalone are recirculated without the addition of fresh air the quality ofthe product is not as good. In order to prevent too high a pressurewithin the dryer and to prevent the building up of too high a percentageof volatiles from the solvents it is necessary to exhaust some of thegases from the dryer. This I preferably do near the entering end becausethe concentration of the solvents is higher at this point and becausethe temperature of the exhausted gases is lower, hence the oven or dryerefficiency will be greater if the gases are exhausted at the coolestpoint. By having the sta tions positioned at different places lengthwiseof the oven the controls may be fixed so that if necessary a uniformtemperature in the dryer may be maintained or the temperature may bevaried lengthwise of the dryer as desired since the temperature of theheating medium is sufficiently high to be able to attain the necessaryworking temperature at any point.

By my method of admission of the heating medium through stations withthe mixing boxes it is possible to control the velocity and quantity ofthe air admitted at each station. This may be accomplished in a varietyof ways such as the initial installation of different size fans orblowers or by control in any-well known manner of the speed of the fan,or by a damper in the conduit or opening from the fan discharge to theplenum chamber.

Referring to the drawings:

Figure 1 is a view in elevation of one-half of the dryer or ovenembodying the principles of my invention.

Figure 1a is a view in longitudinal elevation of the other half of thedryer or oven embodying the principles of my invention.

Figure 2 is a plan view of Figure 1.

Figure 2a is a plan view of Figure 1a.

Figure 3 is a cross sectional view of Fig. 2 along the line 33, lookingin the direction of the arrows.

Figure 4 is a cross sectional view of Figure 2 along the line 4-4,looking in the direction of the arrows.

The dryer or oven I is of metallic construction having insulated walls 2with the usual support ing frames. An endless carrier 3 is adapted to bemotivated in any well known way through the oven. This carrier carriesfingerbars or wickets 4 to receive the metallic sheets which are beingtreated. An indirect heater 5 is preferably positioned on the top of thedryer in order to save floor space but this heater may be stationedalongside of the dryer if required. Indirect heater 5 is of any wellknown type wherein the products of combustion and the heating medium,that is, generally air are not permitted to intermingle. The path of thecirculating heating medium may be described as follows: Fan 6 which maybe driven in any well known manner forces the air through duct 1 intoheater 5 whence it passes to the main distributing duct or headers 8leading to the distributing stations or zones 9, In, H, I2. At each zonethere is a circulating fan 13, which may be driven in any well knownmanner, and a mixing box M communicating with the header 8 and fan l3.Also leading into this mixing box is an adjustable fresh air opening I 5and a return air connection I6. A damper I1 is located in the return airconnection. At each station or zone the air passes from the outlet offan l3 into a duct I 8 leading to a perforated supply duct l9 runninglengthwise of the oven underneath the metallic sheets to be dried. Theair passes from supply duct l9 upward between the sheets into a similarcollector duct 20 whence it goes through air connection Hi to mixing boxM and is recirculated. In the connection from the main header duct 8 toeach mixing box I4 is an automatic damper 2| actuated by a thermostaticelement 22 operating a damper motor 23 in any well known manner tooperate the damper 2|.

At the entering end of the oven is provided a hood 24 having aconnection 25 leading into the inlet of a fan 21. Connection 26leads-from the duct 20 to the fan 21 for delivering air from the duct tothe fan. The air is discharged from fan 21 through duct 28 where it maybe either spilled to atmosphere or recirculated through duct 29 back tothe combustion chamber of heater 5. The proportions of air spilled orrecirculated are con trolled by means of dampers 30 and 3|. There aredampers 32 and 33 on the inlet side of fan 21, damper 32 controlling theamount of air removed from hood 24 and damper 33 controlling the amountof air removed from oven I through duct 20. The amount of air handled byfan 21 is approximately equal to the amount of fresh air and heatingmedium entering the oven. Whereas one fan is shown for handling both theex-- haust from the hood and from the duct 20, it is also possible touse one fan exhausting from the hood only and spilling to atmosphere,and another connection exhausting directly from the duct to thecombustion chamber.on the heater.

The operation of the dryer is as follows:

The endless carrier 3 introduces the metallic sheets into the dryingchamber. The heating .medium from stations 9, H], H, I2, is blown upthrough conduits 19 between and around the r metallic sheets, and afterdrying the sheets, is withdrawn from duct 20. The temperature of theheating medium within the oven at the various points is controlleddependent upon the desired zone temperature as follows:

Some of the exhausted air passes up from duct 20 into connection l6 andthence into mixing chamber 14. Fresh heating medium is simultaneouslyadmitted to the mixing chamber M from the central heater 5 throughconduit 8. The amount of hot heating medium is controlled with respectto each mixing box l4 automatically by thermostatic elements 22 locatedin each zone of the dryer. Fan l3 then circulates the mixture throughconduit I 9. In order to have the highest efiiciency possible, a portionof the air from the oven containing the volatiles is withdrawn from thepoint of greatest concentration and is con ducted through connections25, 26, and moved by fan 21, thence through conduits 28, 29, to furnishpreheated air and volatile fuel to the combustion chamber of theindirect heater.

It should be noted that by this means the volatiles, if explosive, maybe kept down in the recirculated heating medium to a concentration thatwill not be explosive and may be controlled with respect to the desireddegree of concentration. The exhaust air from the oven containing thesevolatiles in passing through the combustion chamber 34 is heated to atemperature of about 1100 Fahrenheit which is above their auto-ignitiontemperature and consequently the fuel value of the volatilesregardlessof concentration is taken advantage of since they must burn at thistemperature. These products of combustion pass around the interchangerin heater 5 thereby giving off their heat to the incoming fresh air fromblower 6. After giving off their heat the products of combustion passthrough duct 35 into fan 36 and are discharged to atmosphere throughstack 31. By burning the volatiles, not only is the heat value recoveredbut also they are discharged through the stack 31 in a form that is lessharmful to the surrounding area. Also the air mixed with the volatilesintroduced through conduit 29 into combustion chamber 34 may be said tobe preheated and thereby increases the efficiency of the heater.Additional fuel, of course, is required in the heater but the amount ismaterially reduced by the utilization of the volatiles. The amount offuel being burned in combustion chamber 34 is controlled by a valve 38in the fuel supply line 39. Valve 38 is actuated by a thermostat 40located in duct 8.. In this way any predetermined temperature may becontinuously maintained in duct 8. In other words, the makeup hotheating medium can be at a constant temperature.

The dryer l is of little use without means for cooling the metallicsheets, since no matter how thoroughly they are dried they will be tackyand difficult to handle as they come from the dryer I. In addition, inmany instances, the surface of the metallic sheets is materiallyimproved by a cooling or chilling process.

At the exit end of the dryer or oven I, I provide a hood or chamber withan exhaust stack 46 to permit the entrained hot drying medium to beexhausted from between the metallic sheets while at the same timeblowing a cooling medium between the sheets thereby enabling a reductionof temperature that can be controlled without harm to the coated surfaceof the sheet. Damper 4] enables the operator to control the amount ofair discharged to atmosphere.

A vent pipe 5| connects with stack 46 before the damper 41. This acts asa pressure relief in the oven to prevent heating medium from spillinginto the cooling zone.

It will thus be seen that I have invented a dryer for metallic sheetsand the like wherein the sheets may be dried in a controlledpredetermined atmosphere of predetermined temperature, wherein thetemperature may be varied or uniform at different parts of the dryer andthe quantity or velocity of the drying medium may be controlled, andwherein relative quantities of fresh and recirculated air as well as thefresh heating medium may be controlled, and wherein the fuel value ofthe solvents may be utilized and the heating value of the waste heatingmedium may also be utilized both in connection with the oven itself andin connectionwith the heater.

What I claim is:

1. A drying oven for metal lithographic plates or the like comprising ahousing, means for conveying said plates or the like through saidhousing, a furnace, a duct leading from said housing to said furnace forconducting to said furnace volatiles given off by said plates in saidhousing, means for heating said furnace to the autoignition temperatureof said volatiles, an indirect heat interchanger in said furnace, meansfor drawing air through said heat interchanger and delivering the sameto different zones in said housing, a mixing box for each zone, a mainhot air distributing duct leading from said indirect heat interchangerto said mixing boxes, ducts for delivering air from each mixing box toits associated housing zone and for returning air from said zone to saidmixing box, and dampers for regulating the supply of hot air to saidmixing boxes and the withdrawal of air from said casing to said furnace.

2. A drying oven for metal lithographic plates or the like comprising ahousing, means for conveying said plates or the like through saidhousing, a furnace, a duct leading from said housing to said furnace forconducting to said furnace volatiles given off by said plates in saidhousing, means for heating said furnace to the autoignition temperatureof said volatiles, an indirect heat interchanger in said furnace, meansfor drawing air through said heat interchanger and delivering the sameto different zones in said housing, a mixing box for each zone, a mainhot air distributing duct leading from said indirect heat interchangertosaid mixing boxes, ducts for delivering air from each mixing box to itsassociated housing zone and for returning air from said zone to saidmixing box, dampers for regulating the supply of hot air to said mixingboxes and the withdrawal of air from said casing to said furnace, andmeans responsive to the temperature in each zone for operating the hotair damper for such zone.

3. A drying oven for metal lithographic plates or the like comprising ahousing, means for conveying plates or the like through said housing,

said housing being divided into zones, a mixing box for each zone, amain hot air distributing duct communicating with said mixing boxes.ducts for delivering air from each mixing box to its associated housingzone and for returning air from said zone to said mixing box, dampersfor regulating a supply of hot air to said mixing boxes, meansresponsive to the temperature of each zone for operating the hot airdamper for said zone, a furnace, an indirect heat exchanger in saidfurnace communicating with said main distributing duct for supplying hotair thereto, a duct leading from said housing to said furnace forconducting to said furnace volatiles given off by the metal plates insaid housing, and means for heating said furnace to the auto-ignitiontemperature of said volatiles.

RALPH BYRON.

